1. Field of the Invention
The invention relates generally to a doping method, configurations of PN junction and manufacturing method and apparatuses of photovoltaic cells for providing solar energy. More particularly, this invention relates to configuration and improved methods for doping PN junctions of back contacted battery cells to simplify the manufacturing methods of photovoltaic cells to capture and provide solar energy.
2. Description of the Prior Art
One of key factors for driving the technological developments in the twenty-first century is the development of renewable energy. A major aspect of the developments is to continue explore and improve the efficiency and economic competiveness among different energy sources of solar energy. Since the technology for capturing and utilizing solar energy is a clean, reliable, low maintenance, noise free, and long term sustainable energy source, governmental policies have also focused on the development of new technologies of solar energy as one of the most important development goals.
With the acceleration of the increased capacity of the photovoltaic energy generation in the past few years, large quantity of solar panels are manufactured and shipped. With the greater demand not al to be fully satisfied by the limited supply, another subject of interest is to improve the energy conversion efficiency and solar cell productivity such that the solar panel shortage issues can be properly resolved. Specifically, the solar energy is generated by exposing the solar cells to light emitting from the sun. The photons in the sun beams are projected and captured by the solar cells wherein the photons have higher energy than the energy-gap between levels of electrons circulating the nuclides thus knocking the electrons off their tracks thus generating free pairs of electrons and holes. With electron and hole pairs generated at higher energy and unstable states, these unstable pairs soon encountered and collide with other nuclides and energy the energy absorbed from photons are converted into heat and electric current or transmitting through the PN junctions of the solar cells as direct current while the heat generated in the processes is energy lost in the energy conversion processes. There is additional electrical conduction and DC-to-AC conversion losses before the solar energy is finally utilized as industrial or household electric energies. Therefore, the efficiency of energy utilizations for solar power is determined by multiple factors including but not limited to the materials of the solar cells, the manufacturing methods and the configurations of the solar cells, and the angles, areas, intensity and the light paths of the sun beams projected onto the solar panels. Instead of placing the solar cells on the front surface that often-block the full absorption of the photons; a recent improvement is to form the solar cells at the back surface of the substrate to reduce the front-surface block off losses. The configuration is often referred to as back contact cell. The doping regions and electrical contacts to the cells are therefore formed near and on the back surface of the substrate. The electrical conduction losses within the substrate especially through the lateral directions are reduced while light collection through the entire front surface can also be conveniently achieved thus greatly increase the efficiency of the solar cells. There are further advantages in cost reduction for producing the solar panels because it is more convenient to package the solar cells formed with back contact configurations.
However, as the solar cells are formed near the back surface of the substrate, the free electron and hole pairs are required to travel through almost the entire thickness to the reach the back surface. For this reason, the silicon substrate must be able to maintain long life for the charged particles travel through the substrate in order to avoid combination of these charge particles before reaching the back surface thus greatly reduces the efficiency of the solar cells due to lower current density. An improved configuration generally referred to as interdigitated back contact (IBC) battery cells is implemented to overcome such technical limitations. In various publications related to manufacturing processes to produce the IBC solar cells, specifically in the manufacturing processes implemented by SUNPOWER, complicated lithographic processes are applied. These processes cause high production costs due to the requirements of multiple masks. For the purpose of reducing the production costs, some manufacturers use the processes of applying masks to form intermixed alternate P-N dopant regions. However, the manufacturing costs are still very high due to the technical issues of applying multiple masks and the precision restrictions for alignment required by lithography. Therefore, there is an urgent need in the art of manufacturing and designing solar cells to provide new and improved manufacturing process with new configurations of the MC solar cell to overcome the above-discussed technical limitations and difficulties.